Re: [PATCH] writeback_inodes can race with unmount

[Mika Penttilä]

Chris Mason wrote:

> There's a small window where the filesystem can be unmounted during
> writeback_inodes.  The end result is the iput done by sync_sb_inodes
> could be done after the FS put_super and and the super has been removed
> from all lists.
>  

Why don't we have the same race in the sync() path as well? Moving the 
locking to sync_sb_inodes() itself would fix it also.

> The fix is to hold the s_umount sem during sync_sb_inodes to make sure
> the FS doesn't get unmounted.
>
> Index: linux.t/fs/fs-writeback.c
> ===================================================================
> --- linux.t.orig/fs/fs-writeback.c	2004-06-08 14:45:49.000000000 -0400
> +++ linux.t/fs/fs-writeback.c	2004-06-08 14:47:58.000000000 -0400
> @@ -360,9 +360,18 @@ restart:
> 	sb = sb_entry(super_blocks.prev);
> 	for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
> 		if (!list_empty(&sb->s_dirty) || !list_empty(&sb->s_io)) {
> +			/* we're making our own get_super here */
> 			sb->s_count++;
> 			spin_unlock(&sb_lock);
> -			sync_sb_inodes(sb, wbc);
> +			/* if we can't get the readlock, there's no sense in
> +			 * waiting around, most of the time the FS is going
> +			 * to be unmounted by the time it is released
> +			 */
> +			if (down_read_trylock(&sb->s_umount)) {
> +				if (sb->s_root)
> +					sync_sb_inodes(sb, wbc);
> +				up_read(&sb->s_umount);
> +			}
> 			spin_lock(&sb_lock);
> 			if (__put_super(sb))
> 				goto restart;
>  

--Mika


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/